How can I run a command, when I press the top button of my Bamboo Ink pen?

Here is how I do it:

ACTION=="add" , SUBSYSTEM=="bluetooth", DEVPATH=="/devices/pci0000:00/0000:00:14.0/usb1/1-10/1-10:1.0/bluetooth/hci0/hci0:3585", RUN+="/home/gvb/bin/run-pen-state.sh" 

What I wanted to do was switch between pen and eraser and in Xournal. The two scripts needed for this are shown below. They need two small utilities: wmctrl and xdotool...

Contents of "run-pen-state.sh" is

#!/bin/csh sudo -u gvb -i /home/gvb/bin/pen-state 

while "pen-state" itself is

#!/usr/bin/perl -w $home=$ENV{'HOME'}; $store=`grep "#state: " ~/bin/pen-state | grep -v store`; chomp($store); $command=`export DISPLAY=:0; export XAUTHORITY=$home/.Xauthority; wmctrl -l`; foreach $line (split(/\n/,$command)){ if (($line=~ /Xournal/)&&($line=~ /$filename/)){ $winid=(split(/ /,$line))[0]; } } if($winid){ system("export DISPLAY=:0; export XAUTHORITY=$home/.Xauthority; wmctrl -i -a $winid"); if($store =~ /pen/){ $now="state: eraser"; system("export DISPLAY=:0; export XAUTHORITY=$home/.Xauthority; xdotool key shift+ctrl+e"); }else{ $now="state: pen"; system("export DISPLAY=:0; export XAUTHORITY=$home/.Xauthority; xdotool key shift+ctrl+p"); } $now="#$now"; print "$store\n"; print "$now\n"; open(SELF,"$home/bin/pen-state"); read(SELF,$self,-s "$home/bin/pen-state",0); close(SELF); $self=~ s/$store/$now/; open(SELF,">$home/bin/pen-state"); print SELF $self; close(SELF); } #state: pen 

Update February 2022:
I just noticed, with Ubuntu 22.04, Kernel 5.16.8 and Gnome 41.3 it works out of the box. The top button is detected as Super+AudioMicMute combo which you can use to assign any shortcut in Gnome settings. But I don't know when it started to work.

Original answer:
I have nearly the same approach as in the previous answer from Guillaume. But the problem with his answer for me is, that I found no way to distinguish which device triggered the add action of the bluetooth subsystem, so that Guillaume's simple rule also matched when I connected any other device via bluetooth. But with my Lenovo active pen 2 I noticed that one of two things can happen, whenever I press the top button.

Case 1) The pen connects and disconnects within one or two seconds. udevadm monitor shows only the add and remove action.

Case 2) After udev's add action the pen is recognized as HID named Lenovo Active Pen2 Keyboard. Then it takes about 10 seconds until it is removed.

ACTION=="add", SUBSYSTEM=="bluetooth", DEVPATH=="/devices/pci0000:00/0000:00:14.0/usb1/1-7/1-7:1.0/bluetooth/hci0/hci0:3585", RUN+="/usr/local/bin/bluetooth_event_detected.sh add" ACTION=="remove", SUBSYSTEM=="bluetooth", DEVPATH=="/devices/pci0000:00/0000:00:14.0/usb1/1-7/1-7:1.0/bluetooth/hci0/hci0:3585", RUN+="/usr/local/bin/bluetooth_event_detected.sh remove" ACTION=="add", SUBSYSTEM=="hid", DEVPATH=="/devices/virtual/misc/uhid/0005:17EF:60A8.*", RUN+="/usr/local/bin/bluetooth_event_detected.sh force" 

So I watch for the add and remove actions in my udev rule, which triggers a script that times how long it takes between an add and the next remove event. If it takes less than 2 seconds it assumes that this was the pen and sets a flag under /tmp/stylus. The same happens in case two when the pen is recognized as HID.

#!/bin/bash # PATH is not provided in an udev environment PATH=/bin:/usr/bin:/usr/local/bin DIRECTORY=/tmp/stylus TSFILE=$DIRECTORY/bluetooth_timestamp BTN_PRESSED_FLAG=$DIRECTORY/stylus_button_pressed TIME_DELTA="2" ACTION=$1 NOW=$(date +%s) mkdir -p $DIRECTORY chmod 777 $DIRECTORY if [ "$ACTION" = "add" ]; then echo $NOW > $TSFILE elif [ "$ACTION" = "remove" ]; then ADDED_TS=$(cat $TSFILE) DIFF=$(($NOW-$ADDED_TS)) echo diff: $DIFF # if the time between adding and removing is # 2 seconds or less, we assume the stylus button # was pressed if [ "$DIFF" -le "$TIME_DELTA" ]; then touch $BTN_PRESSED_FLAG chmod 666 $BTN_PRESSED_FLAG fi elif [ "$ACTION" = "force" ]; then touch $BTN_PRESSED_FLAG chmod 666 $BTN_PRESSED_FLAG fi 

Last I have a simple script autostarted when I log into my desktop environment, that keeps watching for that flag under /tmp/stylus and executes gnome-screenshot -i.

#!/bin/bash FILE=/tmp/stylus/stylus_button_pressed CMD="gnome-screenshot -i" while true; do if [ -f $FILE ]; then echo running command $CMD rm $FILE fi sleep 0.1 done 

Not elegant, but working.